Recently, a demand for precision management of a circuit line width required for semiconductor elements has been increasingly high. A reduced projection lithography device referred to as a so-called stepper exposes and transfers a pattern onto a wafer with an original pattern including a circuit pattern formed (also referred to a photolithography mask or a reticle, and, hereinafter, collectively referred to as a mask) to form a circuit, so that the semiconductor elements are manufactured. Therefore, a pattern drawing apparatus using an electron beam capable of drawing a fine circuit pattern is used in order to manufacture the mask for transferring the fine circuit pattern onto the wafer. The pattern drawing apparatus may be used to directly draw a pattern circuit onto a wafer.
Improvement in yield is necessary for the manufacture of LSI, such as a central processing unit (CPU) or a field programmable gate array (FPGA), involving significant manufacturing costs. One main factor that causes the yield to be reduced is a pattern defect of a mask used in exposing and transferring an ultra-fine pattern onto a semiconductor wafer with a photolithography technique. Recently, a scale required to be detected as a pattern defect has been considerably small as an LSI pattern scale to be formed on a semiconductor wafer has been miniaturized. Therefore, a pattern inspection apparatus that inspects a defect of a transferring mask used in manufacturing LSI desirably increases in precision.
A method of performing inspection by comparing an optical image including a pattern formed on a sample, such as a photolithography mask, captured at a predetermined magnification with a magnification optical system, to designed pattern data or an optical image including a pattern of the same kind on the sample, captured, has been known as an inspection method. Examples of a pattern inspection method include “die to die inspection” including: comparing pieces of optical image data each including a pattern of the same kind captured at a different position on the same mask, and “die to database inspection” including: inputting drawing data (pattern data) including pattern-designed CAD data converted into an apparatus input format to be input into a drawing apparatus in drawing a pattern onto a mask, into an inspection apparatus; generating designed image data (a reference image) based on the drawing data; and comparing an optical image including the pattern captured, being measurement data, to the designed image data. In the inspection method in the inspection apparatus, a sample is mounted on a stage and then the stage moves, so that a light beam scans on the sample and the inspection is performed. A light source and an illuminating optical system irradiate the sample with the light beam. Light transmitted through or reflected from the sample forms an image on a photodetector through an optical system. The image captured by the photodetector is transmitted as measurement data to a comparative circuit. The comparative circuit compares the measurement data and the reference data in accordance with an appropriate algorithm after positioning between the images, and determines that a pattern defect is present when inconsistency is acquired.